Surface Motion of Tympanic Membrane in a Chinchilla Model of Acute Otitis Media

Finite-element modelling of interactions of needle with tympanic membrane and middle ear

The tympanic membrane (TM) is one of the most common routes to access the middle ear and inner ear for the treatment of hearing and balance pathologies. Since the TM is a soft thin biological tissue with small dimensions, using needles seems to be among the most practical interventional approaches. In this study, we proposed a finite-element (FE) analysis of needle-TM interactions that combines a 3D model of the TM and other main middle-ear structures in gerbil, and a 2D model of needle insertion into the TM based on the cohesive zone method (CZM). The TM was modelled using a 1st-order Ogden hyperelastic material and its properties were obtained by fitting to the experimental force-displacement plots of large deformation in the TM under needle indentation. The cohesive parameters were also acquired by calibrating the puncture force against the experimental data of needle insertion into the TM. These FE models were then used to obtain the deformation behaviour of the TM and other middle-ear structures due to the insertion force applied at different locations on the TM. Moreover, we investigated the effect of the TM thickness, the geometry of the needle (i.e., diameter and tip angle), and needle material on the insertion of needles into the TM. We also studied the penetration success of deformable needles.

Experimental Study of Needle Insertion into Gerbil Tympanic Membrane

The perforation characteristics and fracture-related mechanical properties of the tympanic membrane (TM) greatly affect surgical procedures like myringotomy and tympanostomy performed on the middle ear. We analyzed the most important features of the gerbil TM perforation using an experimental approach that was based on force measurement during a 2-cycle needle insertion/extraction process. Fracture energy, friction energy, strain energy, and hysteresis loss were taken into consideration for the analysis of the different stages of needle insertion and extraction. The results demonstrated that (1) although the TM shows viscoelastic behavior, the contribution of hysteresis loss was negligible compared to other irreversible dissipated energy components (i.e., fracture energy and friction energy). (2) The TM puncture force did not substantially change during the first hours after animal death, but interestingly, it increased after 1 week due to the drying effects of soft tissue. (3) The needle geometry affected the crack length and the most important features of the force-displacement plot for the needle insertion process (puncture force, puncture displacement, and jump-in force) increased with increasing needle diameter, whereas the insertion velocity only changed the puncture and jump-in forces (both increased with increasing insertion velocity) and did not have a noticeable effect on the puncture displacement. (4) The fracture toughness of the gerbil TM was almost independent of the needle geometry and was found to be around 0.33 ± 0.10 kJ/m2.

Optical coherence tomographic measurements of the sound-induced motion of the ossicular chain in chinchillas: Additional modes of ossicular motion enhance the mechanical response of the chinchilla middle ear at higher frequencies

Wavelength-swept optical coherence tomography (OCT) was used to scan the structure of cadaveric chinchilla ears in three dimensions with high spatial resolution and measure the sound-induced displacements of the entire OCT-visible lateral surfaces of the ossicles in the lateral-to-medial direction. The simultaneous measurement of structure and displacement allowed a precise match between the observed motion and its structural origin. The structure and measured displacements are consistent with previously published data. The coincident detailed structural and motion measurements demonstrate the presence of several frequency-dependent modes of ossicular motion, including: (i) rotation about an anteriorly-to-posteriorly directed axis positioned near the commonly defined anatomical axis of rotation that dominates at frequencies below 8 kHz, (ii) a lateral-to-medial translational component that is visible at frequencies from 2 to greater than 10 kHz, and (iii) a newly described rotational mode around an inferiorly-to-superiorly directed axis that parallels the manubrium of the malleus and dominates ossicular motion between 10 and 16 kHz. This new axis of rotation is located near the posterior edge of the manubrium. The onset of the second rotational mode leads to a boost in the magnitude of sound-induced stapes displacement near 14 kHz, and adds a half-cycle to the accumulating phase in middle-ear sound transmission. Similar measurements in one ear after interruption of the incudostapedial joint suggest the load of the cochlea and stapes annular ligament is important to the presence of the second rotational mode, and acts to limit simple ossicular translation.

Panel 1: Biotechnology, biomedical engineering and new models of otitis media

OBJECTIVE

To summarize recently published key articles on the topics of biomedical engineering, biotechnology and new models in relation to otitis media (OM).

DATA SOURCES

Electronic databases: PubMed, Ovid Medline, Cochrane Library and Clinical Evidence (BMJ Publishing).

REVIEW METHODS

Articles on biomedical engineering, biotechnology, material science, mechanical and animal models in OM published between May 2015 and May 2019 were identified and subjected to review. A total of 132 articles were ultimately included.

RESULTS

New imaging technologies for the tympanic membrane (TM) and the middle ear cavity are being developed to assess TM thickness, identify biofilms and differentiate types of middle ear effusions. Artificial intelligence (AI) has been applied to train software programs to diagnose OM with a high degree of certainty. Genetically modified mice models for OM have further investigated what predisposes some individuals to OM and consequent hearing loss. New vaccine candidates protecting against major otopathogens are being explored and developed, especially combined vaccines, targeting more than one pathogen. Transcutaneous vaccination against non-typeable Haemophilus influenzae has been successfully tried in a chinchilla model. In terms of treatment, novel technologies for trans-tympanic drug delivery are entering the clinical domain. Various growth factors and grafting materials aimed at improving healing of TM perforations show promising results in animal models.

CONCLUSION

New technologies and AI applications to improve the diagnosis of OM have shown promise in pre-clinical models and are gradually entering the clinical domain. So are novel vaccines and drug delivery approaches that may allow local treatment of OM.

IMPLICATIONS FOR PRACTICE

New diagnostic methods, potential vaccine candidates and the novel trans-tympanic drug delivery show promising results, but are not yet adapted to clinical use.

The chinchilla animal model for hearing science and noise-induced hearing loss

The chinchilla animal model for noise-induced hearing loss has an extensive history spanning more than 50 years. Many behavioral, anatomical, and physiological characteristics of the chinchilla make it a valuable animal model for hearing science. These include similarities with human hearing frequency and intensity sensitivity, the ability to be trained behaviorally with acoustic stimuli relevant to human hearing, a docile nature that allows many physiological measures to be made in an awake state, physiological robustness that allows for data to be collected from all levels of the auditory system, and the ability to model various types of conductive and sensorineural hearing losses that mimic pathologies observed in humans. Given these attributes, chinchillas have been used repeatedly to study anatomical, physiological, and behavioral effects of continuous and impulse noise exposures that produce either temporary or permanent threshold shifts. Based on the mechanistic insights from noise-exposure studies, chinchillas have also been used in pre-clinical drug studies for the prevention and rescue of noise-induced hearing loss. This review paper highlights the role of the chinchilla model in hearing science, its important contributions, and its advantages and limitations.

Surface Motion Changes of Tympanic Membrane Damaged by Blast Waves

Eardrum or tympanic membrane (TM) is a multilayer soft tissue membrane located at the end of the ear canal to receive sound pressure and transport the sound into the middle ear and cochlea. Recent studies reported that the TM microstructure and mechanical properties varied after the ear was exposed to blast overpressure. However, the impact of such biomechanical changes of the TM on its movement for sound transmission has not been investigated. This paper reports the full-field surface motion of the human TM using the scanning laser Doppler vibrometry in human temporal bones under normal and postblast conditions. An increase of the TM displacement after blast exposure was observed in the posterior region of the TM in four temporal bone samples at the frequencies between 3 and 4 kHz. A finite element model of human TM with multilayer microstructure and orthogonal fiber network was created to simulate the TM damaged by blast waves. The consistency between the experimental data and the model-derived TM surface motion suggests that the tissue injuries were resulted from a combination of mechanical property change and regional discontinuity of collagen fibers. This study provides the evidences of surface motion changes of the TM damaged by blast waves and possible fiber damage locations.